Try the time command (not the shell builtin): $ command time -f 'max resident:\t%M KiB' ls / bin etc initrd.img.old lib32 media proc sbin

Try the time command (not the shell builtin): $ command time -f 'max resident:\t%M KiB' ls / bin etc initrd.img.old lib32 media proc sbin tmp vmlinuz boot home iso lib64 mnt root srv usr vmlinuz.old dev initrd.img lib lost+found opt run sys var max resident: 968 KiB